Nucleating agents for thermoplastic resins

ABSTRACT

This invention relates to the use of a special class of sulfonic and phosphonic acids, and salts of the acids, to give improved nucleation for foam extrusion of thermoplastics using either dissolved gas or chemical blowing agents to produce foam.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 07/312,989, filedFeb. 17, 1989 and allowed Apr. 10, 1989.

FIELD OF THE INVENTION

This invention relates to the use of a special class of sulfonic andphosphonic acids, and salts of the acids, to give improved nucleationfor foam extrusion of thermoplastics using either dissolved gas orchemical blowing agents to produce foam.

BACKGROUND OF THE INVENTION

Conductive wire is often used to transmit electronic signals. The wiremust be protected, or insulated, and thermoplastic coatings areordinarily used for this. The thermoplastic is extruded from a moltenstate onto and around the wire. The thermoplastic materials are selectedon the basis of having a low dielectric constant and a low dissipationfactor. It has previously been found that if the thermoplastic materialis foamed as it is applied to the wire, the dielectric constant isdesirably lowered, due to the formation of numerous smallnon-interconnected cells in the foam. In U.S. Pat. No. 3,072,583 isdisclosed a nucleated foaming process for extruding perfluorinatedpolymer foam around transmission wire with a dissolved gas blowingagent. Foamed insulation using other thermoplastic materials, especiallypolyolefins, is also widely used.

A nucleating agent is needed in the foaming process to achieve uniform,small-diameter cell structure. A preferred art-recognized nucleatingagent for fluoropolymer resin is boron nitride, an inert white ceramicpowder. A 0.5-2.0 weight loading of boron nitride, based on polymer,normally provides adequate foam cell nucleation. The lower the specificgravity of the molten resin, the more nucleant is needed, on a weightbasis. Thus, an ethylene(E)/tetrafluoroethylene(TFE) copolymer(ETFEcopolymer) with a melt specific gravity of about 1.3 requires morenucleant than a tetrafluoroethylene(TFE)/hexafluoropropylene(HFP)copolymer(TFE/HFP copolymer) at a melt specific gravity of 1.6.

U.S. Pat. No. 4,764,538 discloses synergistic combinations of boronnitride and certain inorganic salts which give greatly enhanced foamnucleation in fluoropolymers This combination not only allows asignificant reduction in the amount of boron nitride needed but alsogives improved foam in terms of smaller cells. Improved capacitance anddiameter uniformity are also attained.

The present invention provides a special class of sulfonic andphosphonic acids, and salts of the acids, which give very efficientnucleation of a wide variety of thermoplastic materials at lowconcentrations without the use of boron nitride or any other traditionaltype of nucleating agent.

As used herein the term "thermoplastic" means and is intended to includeany organic material that is rendered soft and moldable by applicationof heat (Hackh's Chemical Dictionary, Julius Grant, 4th edition,McGraw-Hill Book Company, New York, N.Y.). Other terms used synonymouslyherein with "thermoplastic" and "thermoplastic material" are"thermoplastic resin" and "polymer," it being understood that the resinor polymer must be capable of being rendered soft and moldable byapplication of heat, that is, it is melt processible. The term"composition" as it is used herein is intended to include thethermoplastic material and other ingredients or additives which,individually, may or may not be melt processible, as will be discussedin greater detail in the Detailed Description of the Invention.

The compositions of this invention are useful in producing foams forother applications as well as for wire coating. Such examples include,but are not intended to be limited to, foamed sheet for electricalinsulation, heat insulation and cushioning; foamed pipe and tubing; andinjection molded pieces.

SUMMARY OF THE INVENTION

This invention resides in a foamable thermoplastic resin compositioncontaining as a nucleating agent a nucleating-effective amount of atleast one compound which is thermally stable at the melt temperature ofthe extrusion and is selected from sulfonic and phosphonic acids, andsalts of the acids, which compositions significantly enhance foamnucleation, as evidenced by smaller foam cells, higher foam voidcontents, and/or greater uniformity of cell size. These compositionscontain 50 to 8000 ppm, preferably 250 to 3000 ppm, by weight, for mostcompositions, of one or more of the acids and/or salts which are of theformula

    [Z(CF.sub.2)×(CF.sub.2 CFX).sub.p (R').sub.y (CH.sub.2).sub.z R0.sub.3 ].sub.n M

wherein:

the bivalent groups, except for RO₃, may be present in any sequence;

Z is CCl₃, CCl₂ H, H, F, Cl or Br;

each X, independently, is H, F, Cl or CF₃ ;

R is sulfur or phosphorus;

M is H or a metallic, ammonium, substituted ammonium or quaternaryammonium cation;

each of x and z, independently, is an integer and is 0 to 20;

p is an integer and is 0 to 6;

y is 0 or 1;

x+y+z+p is a positive integer or, if x +y+z+p is 0, Z is CCl₃ or CCl₂ H;

n is the valence of M; and

R' is selected from

a C₅₋₆ perfluorinated alicyclic ring diradical;

a C₁₋₁₆ perfluorinated aliphatic polyether diradical with repeat unitsselected from [CF₂ 0], [CF₂ CF₂ 0], and [CF₂ CF(CF₃)0]; and

a substituted or unsubstituted aromatic diradical, in which case, Z isH.

By "foamable, thermoplastic resin composition" is meant anythermoplastic resin composition that is foamable by means of a gasinjection process or through use of a chemical blowing agent.

Preferably, M is a metallic cation. When M is H, the resultant sulfonicor phosphonic acid may not be effective in all thermoplastic resincompositions. When M is selected so as to be other than a metalliccation or H, it preferably should be such that the resulting nucleatingagent is stable at the foam processing temperature. Failure to providesuch consideration in the selection of M may lead to in situdecomposition of the cationic moiety, with resultant conversion of M toH. The significance of this aspect of the invention will be readilyunderstood in view of the significance of M on the foaming process, asdescribed hereinafter in the Detailed Description of the Invention.

The stability of the nucleating agent at the foam processing temperaturemust be considered not only in connection with the selection of M butalso in connection with the selection of the other symbols in the aboveformula. More specifically, it is to be understood that the nucleatingagent should be stable at the foam processing temperature which can varysubstantially depending on the thermoplastic being foamed. Thus, in theabove formula, when each of x, pand y is 0, z is 1 to 10 and Z is CC1₃or CCl₂ H, the resultant nucleating agent, for example, trichloroethanesulfonic acid or its M salt will be stable at normal polyethylenefoam-processing temperatures, such as below about 315° C., but it willnot be stable at the temperature needed to foam high-meltingthermoplastics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides graphical data which may be used in the selection of Min the formula for the nucleating agent (a TBSA salt, definedhereinafter) in the foaming of TFE/HFP copolymer. FIG. 2 providesgraphical data which may be used in the selection of M in the formulafor the nucleating agent (a TBSA salt) in the foaming of polyethylene.

DETAILED DESCRIPTION OF THE INVENTION

The thermoplastic resins useful in the present invention include allsuch resins which can be foamed by a gas injection process and/or by useof a chemical blowing agent. In particular, suitable thermoplastics arethose with a dielectric constant of less than 18, preferably less than12, for example, 10.2 (Example 15 herein). Especially suitable formaking foamed electrical insulation by this invention are those resinswith a dielectric constant of less than 3. Following is a list ofthermoplastic materials, most of which are commercially available, andtheir dielectric constants relative to air having a dielectric constantof 1.0:

    ______________________________________                                        PTFE or TFE/HFP Copolymer                                                                              2.0                                                  TFE/PAVE Copolymer       2.1                                                  Polypropylene            2.25                                                 Polyallomers             2.25                                                 Polyethylene             2.3                                                  ETFE Copolymer           2.6                                                  E/CTFE Copolymer         2.6                                                  EVA Copolymer            2.75-2.8                                             Polycarbonate            2.96                                                 Polyimide                3.0-3.5                                              Polysulfone              3.13                                                 PVC                      4.5-5.8                                              Nylon                    4.5                                                  PVF.sub.2                2.98-8.4                                             Urethanes                6.7-7.5                                              Neoprene @ 1000 KM       16-17                                                ______________________________________                                    

Preferred examples of suitable thermoplastics include melt processiblefluoropolymers; polyolefins; copolymers of alpha-olefins and alpha,beta-unsaturated carboxylic acids having 3 to 8 carbon atoms, and theirmetal salts of Groups I to III of the Periodic Chart of the Elements.Examples of other operable thermoplastics include polystyrenes;polyamides; polyesters; vinyl polymers, such as polyvinyl chloride;uncured naturaland synthetic rubbers; and the broad class of resinsknown as thermoplastic elastomers. It is to be further understood thatthe thermoplastic resins which are useful herein include copolymers suchas styrene copolymers, acrylonitrile/butadiene/styrene polymers, andblends thereof, and blends of polymers with non-polymeric materials, forexample, pigments, fire retardants, minerals and carbon, that is, anymaterial commonly present in foamed compositions. In other words, theinvention is useful with any virgin or blended resin that is capable ofbeing foamed by a gas injection process or by means of a chemicalblowing agent.

Foamed fluoropolymer wire insulation, one of the preferred embodimentsof this invention, is generally produced in the art by a continuous, gasinjection process using chlorodifluoromethane(F-22), nitrogen, carbondioxide, or other gas or gas mixture which is soluble in the moltenresin, using an extruder screw designed for foam operations, and usingboron nitride as a nucleating agent. In such processes the gas dissolvesin the molten resin inside the extruder. Absorption follows Henry's GasLaw which states that the equilibrium value of the mole fraction of gasdissolved in a liquid is directly proportional to the partial pressureof the gas above the liquid surface. By adjusting the gas pressure inthe extruder, the amount of gas dissolved in the melt can be controlled.Generally, the greater the amount of gas dissolved in the melt, thegreater the void volume in the resulting foam.

Chlorodifluoromethane(F-22) is especially suited for foaming because iteasily dissolves in molten fluoropolymer resins, and its thermalstability is adequate to survive the holdup time in the extruder whenmixed with molten resin at temperatures up to 380° C.

As an alternative process, a chemical blowing agent (a chemical which isunstable at the polymer processing temperature and liberates a gas, suchas nitrogen, carbon dioxide or hydrogen) can be incorporated into thethermoplastic to provide the dissolved gas which causes bubbleformation.

Foam cell formation actually starts shortly after the molten resincontaining the blowing agent passes out of the extrusion die. The gasdissolved in the molten resin comes out of solution because of thesudden drop in melt pressure as the extrudate exits the extrusion die.As shown in U.S. Pat. No. 4,764,538, extrusion speed and drawdowninfluence foaming. The polymer is solidified when the extrudate enterswater in a cooling trough, stopping foam cell growth.

A nucleating agent is needed to achieve uniform, small-diameter cellstructure. The preferred commonly used nucleating agent forfluoropolymer resins has been boron nitride, an inert white ceramicpowder. The present invention covers a special family of sulfonic andphosphonic acids, and salts of the acids, which give very efficientnucleation at low concentrations. The optimum nucleating agent andconcentration depend on the specific polymer and conditions employed inthe foaming process.

The nucleating agent of this invention can be blended with virgin orblended polymers, as powder or pellets, and extruded to give ahomogeneous composition containing the desired amount of the nucleatingagent, generally 50-8000 ppm, preferably 250-3000 ppm. Alternatively,the agent can be added to the virgin or blended polymer as a concentratewhich may contain 5-20 times the desired amount of nucleating agent, andthen the concentrate is mixed with 20-5 parts of virgin or blendedpolymer before the foaming step.

With chemically blown compositions the blowing agent and nucleatingagent can be blended with virgin or blended polymer powder and eithercompacted into pellets at room temperature to avoid prematuredecomposition of the blowing agent, or extrusion-compounded at atemperature at which the blowing agent is not decomposed to asubstantial extent.

FIG. 1 and Examples 2 and 3 show how routine experimentation can helpselect the best cation for foaming a particular resin (TFE/HFPcopolymer) with a room temperature dielectric constant of 2.05 with CHF₂Cl using a salt of Telomer B sulfonic acid(TBSA). Telomer B sulfonicacid is of the formula F(CF₂)_(n) CH₂ CH₂ SO₃ H wherein n is a mixtureof 6, 8, 10 and possibly 12, predominantly 8. The results for differentcations are plotted on the FIG. 1 graph using the atomic radius of thecation as abscissa and cation valence as ordinate; above the point foreach cation is shown the minimum average diameter of the foam cells inmicrometers for the optimum concentration tested. It is desirable tohave very small cells and high foam void content. It can be seen in FIG.1 that the cations giving cell diameters equal to or less than about 200micrometers fall between the two outer lines (the preferred range). Thecations giving still smaller cell diameters, equal to or less 75micrometers, fall between the two inner lines (optimum range). As isapparent, for TFE/HFP copolymer the best cations are Zr⁺⁺⁺⁺, Fe⁺⁺⁺, andBa⁺⁺. The preferred nucleating agent concentration for these cationswith thiscopolymer is 500-2000 ppm. Thus, FIG. 1 provides a means forpredicting how other salts of TBSA will perform in TFE/HFP copolymerswith CHF₂ Cl as blowing agent. Similar performance is observed when thethermoplastic resin is a copolymer of tetrafluoroethylene and aperfluoro(alkyl vinyl ether), such as perfluoro(propyl vinyl ether).

Table 1 which follows shows the great difference in nucleatingefficiency of various bivalent salts of TBSA in the experiments depictedin FIG. 1. It also shows that efficient nucleation results in both highvoid content in the foam and small diameters of the foam cells.

In Table 1 and in all the remaining tables herein, the followingabbreviations are used:

SPC: Specific Void Content

AFCD: Average Foam Cell Diameter (at mid-wall)

M: Micrometers

%V: % Voids in Foam as Calculated from the Measured Dielectric Constant

cm³ : Cell Count/cm³ at the Specific Void Content

Conc.: Concentration

Ex St: Extrusion Stability

DC: Dielectric Constant

FCC: Foam Core Capacitance (lowest value)

pF/m: Picofarads/meter

C: Capacitance

                  TABLE 1                                                         ______________________________________                                        TBSA                           AFCD                                           Salt      cc/cm.sup.3   % V    (M)                                            ______________________________________                                        Barium    2,300,000     55      75                                            Strontium 763,000       59     100                                            Calcium   72,200        41     220                                            Zinc      24,800        20     508                                            ______________________________________                                    

FIG. 2 and Example 11 show a similar plot for a polyethylene which has aroom temperature electric constant of 2.3. Salts of the same TBSA (as inFIG. 1 and Examples 2 and 3) were used, with nitrogen as the blowingagent. FIG. 2 has the same general appearance as FIG. 1, but a narroweroptimum range has been chosen (cell diameters equal to or less thanabout 50 micrometers), and the polymer and blowing agent are different.FIG. 2 shows that with this polyethylene the preferred TBSA salts arethose of Cr⁺⁺⁺, Fe⁺⁺⁺, and Ca⁺⁺. The preferred nucleating agentconcentration for these cations with this polymer is 1000-3000 ppm.

One might expect that fluorine-free salts, such as sodium laurylsulfate, would be effective nucleating agents for polyethylene, just asthe fluorine-containing salts of this invention are for fluoropolymers.Surprisingly, this is not always the case, as shown by ComparativeExample B between Examples 11 and 12 herein. Comparative Examples A andB show, also, the inoperability of other compounds as nucleating agents.

Also demonstrated in the examples herein are foamed compositionscomprising ethylene/tetrafluoroethylene copolymers. Preferred nucleatingagents for such resins include the calcium salt of Telomer B sulfonicacid and the potassium salt of a perfluorinated alkane sulfonic acid of1-10 carbon atoms. A preferred concentration of such nucleating agents,based on the composition, is 1000 to 3000 ppm.

The broad applicability of the invention is further demonstrated in theexamples using polyolefins as the thermoplastic resin. Examples ofpolyolefins include, but are not limited to, polyethylenes, linear andbranched, low density and high density. Blends of polyethylenes, andblends of polyethylene or polyethylenes with other thermoplastic resinsare operable herein. Preferred nucleating agents withpolyethylene-containing thermoplastic resins are the potassium salt ofperfluorooctane sulfonic acid, and the calcium, iron or chromium salt ofTBSA, at a preferred concentration of 1000 to 3000 ppm, based on thecomposition.

In general, polymers having high dielectric constants respond best toTBSA salts with small cation radius and low valence. As the acidstrength and/or chain length of the salt anion change in any givenpolymer, the optimum cation also tends to change. In the polyethylene ofExample 11 the optimum cation for a TBSA salt is chromium, whereas witha perfluorooctanesulfonic acid the optimum cation is potassium; withtrifluoromethanesulfonic acid, sodium is the best cation of thosetested. Thus, as the strength of the sulfonic acid increases and/orchain length decreases, the optimum cation moves down or to the left ina plot, such as in FIG. 2. The phosphonic acids, and their salts, ofthis invention give results similar to those described above for thesulfonic acids and their salts. It is to be understood that routineexperimentation may be required to find the optimum cation and anion foreach thermoplastic, with dependence also on variables such as themolecular weight distribution of the thermoplastic, the polarity of thegas used, and the extrusion temperature. However, as demonstratedherein, efficient nucleation is achievable with the nucleating agents ofthe invention in a wide varietyof polymers.

The present invention provides means for producing foamed thermoplasticshaving a combination of a uniformly small cell size, less than 400micrometers, and a very high void content, greater than 50%. Forexample, using TFE/HFP copolymer thermoplastics, cell sizes of less than100 micrometers (average) and void contents of greater than 60% can beachieved. Using polyethylene thermoplastics, cell sizes of less than 100micrometers (average) and void contents of greater than 50% can beachieved. Foams of similar structure (as with polyethylenes) can also beproduced using E/TFE copolymers as the thermoplastic.

EXPERIMENTAL DETAILS

In the examples herein the foaming process was carried out by either acontinuous gas injection foaming process or by extruding a compositioncontaining a chemical blowing agent in the same extruder, with no gasinjection.

The continuous gas injection foaming process was normally carried outusing chlorodifluoromethane (F-22) or nitrogen as the blowing agent.Other known blowing agents could be used to give substantially the sameresults. The foam void level was controlled by the pressure of theblowing agent. The extruder screw design allowed for gas injection andhad a mixing torpedo (as disclosed in U.S. Pat. No. 3,006,029) toprovide a uniform melt. This mixing torpedo allowed each resin cubeblend to become a uniform melt mixture while traversing the length ofthe screw.

Nucleated compositions for the gas injection process can be prepared bycube blending of the resin (melt cut or strand cut) with a nucleatingagent concentrate prepared by blending the sulfonic or phosphonic acid,or its salt, in the form of a powder, with resin powder and/or cubes,and extruding on a 28 mm Werner & Pfleiderer (W&P) twin screw extruderwith a strand cutter to pelletize. The resulting cube blends were feddirectly to the wire coating extruder hopper.

ETFE copolymer compositions containing chemical blowing agents wereprepared by blending the chemical blowing agent and nucleating agentwith polymer powder and compacting into cylindrical pellets about 3 mmin diameter and 6 mm in length with a lab model California Pellet Mill.These pellets were fed directly to the wire coating extruder hopper.

Foam cell size was determined at mid-wall of the foam by visualexamination with a microscope or by taking a picture of a thin sectionof foamed wireinsulation at 20-30X magnification and visuallydetermining average cell size. In some examples the number of cells/cm³is also given. This value is calculated from the foam void level and theaverage cell diameter.

Additional abbreviations used in the examples are shown in Table 2. Inreciting specific polymer compositions in the table, there is no intentto limit the scope of the polymers operable herein to those specificcompositions. Typical conditions used in the examples that follow areshown in Table 3. Regarding Table 3, in Column C a Maillefer extruderwas used to produce the foam and an Entwistle extruder was used toproduce the skin. In Column H the extruder was a Davis-Standard. In allother columns the extruder was an Entwistle. Further regarding Table 3,in Column A, a B&H 75 crosshead was used; in all other columns thecrosshead was a Maillefer 4/6F. Finally, the Column C conditions werecarried out to produce a foam-skin construction, using two extruders anda single crosshead.

Foam cell size depends not only on the nucleating agent, but also onother variables, such as wire speed and, in the case of melt drawextrusion, cone length (the distance from the die exit to the pointwhere the molten tubular polymer forms on the wire), as explained inU.S. Pat. No. 4,764,538. Cone length is related to the applied vacuuminside the cone.

                  TABLE 2                                                         ______________________________________                                        TFE/HFP copolymer                                                                           a copolymer of 12.3 wt % HFP and                                              the balance TFE with a melt flow                                              rate of 6.6 at 372° C. as                                              measured by ASTM D-2116-83                                      PAVE          perfluoro(alkyl vinyl ether)                                    EVA           Ethylene/Vinyl Acetate                                          PVF.sub.2     Poly(vinylidene fluoride)                                       boron nitride SHP-325 grade from Carborundum                                                Corp., having a BET surface area                                              of 8.6 m.sup.2 /g                                               polyarylate   aromatic polyester of Bisphenol                                               A and isophthalic acid, with a                                                melt viscosity at 330° C. of 1600 Pa · s                      at 100 sec.sup.-1 and 2800 Pa · s                                    at 10 sec.sup.-1                                                E/TFE copolymer                                                                             copolymer of 19.6 wt % ethylene,                                              2.2 wt % perfluorobutyl                                                       ethylene, and the balance TFE,                                                with a melt flow rate of 14 at                                                297° C. by ASTM D-3159-83                                Ficel ®   Ficel ® AF-100 formulated zinc                                            compound, a chemical blowing                                                  agent from Sherex Chemical Co.                                  Expandex ®                                                                              Expandex ® 175, barium salt of                                            5-phenyl tetrazole, a chemical                                                blowing agent of Olin Chemicals,                                              Stamford, Connecticut                                           TFE/PPVE(1)   copolymer of TFE and 3.9 wt. %                                  copolymer     perfluoro(propyl vinyl ether),                                                with a melt viscosity of 2.2 ×                                          10.sup.4 poise at 372° C.                                TFE/PPVE(2)   copolymer of TFE and 3.9 wt. %                                  copolymer     perfluoro(propyl vinyl ether),                                                with a melt viscosity of 4.25 ×                                         10.sup.4 poise at 372° C.                                E/CTFE copolymer                                                                            copolymer of ethylene and                                                     chlorotrifluoroethylene                                         FEP copolymer copolymer of TFE and 12.3 wt. %                                               hexafluoropropylene, with a melt                                              flow rate of 6.6 at 372° C. (ASTM                                      D-2116-83)                                                      ZrS-10        zirconium (+4) salt of TBSA                                     CrS-10        chromium (+3) salt of TBSA                                      CeS-10        cerium (+4) salt of TBSA                                        KS-10         potassium salt of TBSA                                          HS-10         TBSA                                                            AS-10         aluminum salt of TBSA                                           SrS-10        strontium salt of TBSA                                          CaS-10        calcium salt of TBSA                                            ZnS-10        zinc salt of TBSA                                               BaS-10        barium salt of TBSA                                             LS-10         lithium salt of TBSA                                            FS-10         iron (+3) salt of TBSA                                          TEAS-10       triethyl amine salt of TBSA                                     BS-6A         barium p-(perfluoro[1,3-                                                      dimethylbutyl]) benzene sulfonate                               BS-9A         barium p-(perfluoro[1,3,5-                                                    trimethylhexyl]) benzene sulfonate                              BaS-A1(H)     barium p-toluene sulfonate                                      BaP-A         barium benzene phosphonate                                      NaP-A         sodium benzene phosphonate                                      NaS-A(II)     4,5-dihydroxy-m-benzene                                                       disulfonic acid disodium salt                                   BS-8          barium perfluorooctane sulfonate                                KS-8          potassium perfluorooctane                                                     sulfonate                                                       KS-8C         potassium perfluorocyclo-                                                     hexylethane sulfonate                                           NaS-1         sodium trifluoromethane                                                       sulfonate                                                       KS-1          potassium trifluoromethane                                                    sulfonate                                                       KS-1(H)       potassium methane sulfonate                                     BaS-3(H)      barium propane sulfonate                                        NaTCA         sodium trichloroacetate                                         BTBP          barium salt of F(CF.sub.2).sub.n CH.sub.2 CH.sub.2 PO.sub.3                   H                                                                             wherein n is a mixture of 6, 8,                                               10 and possibly 12,                                                           predominantly 8                                                 NTBP          sodium salt of F(CF.sub.2).sub.n CH.sub.2 CH.sub.2 PO.sub.3                   H                                                                             wherein n is a mixture of 6, 8,                                               10 and possibly 12,                                                           predominantly 8                                                 LL1121B       barium perfluoro(2,5-                                                         dimethyl)-3,6-dioxatridecanoate                                 BC14(06)      barium perfluoro 3,5,7,9,11,13-                                               hexaoxatetradecanoate                                           BS-12(H)      barium lauryl sulfate                                           NS-12(H)      sodium lauryl sulfate                                           CC-18(H)      calcium stearate                                                BaC-8         barium perfluorooctanoate                                       BaC-9         barium perfluorononanoate                                       AWG-26        Solid copper wire 404                                                         micrometers in diameter                                         AWG-24        Solid copper wire 510                                                         micrometers in diameter                                         AWG-22        Solid copper wire 635                                                         micrometers in diameter                                         ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________                 A         B         C         D         E                        __________________________________________________________________________    Type Foaming Gas Injection, F-22                                                                     Gas Injection, F-22                                                                     Gas Injection, F-22                                                                     Gas Injection,                                                                          Chemical Blow            Extruder Diameter (mm)                                                                     31.75     31.75     60 mm 25.4                                                                              31.75     31.75                    L/D Ratio    30/1      30/1      30/1  20/1                                                                              30/1      30/1                     Type Extrusion                                                                             Melt Draw Pressure  Pressure  Pressure  Pressure                 Screw Design Zone                                                             Feed         4.06/10   3.81/10   4.45/10                                                                             4.57/12                                                                           3.81/10   6.6/13                   Metering     1.02/4    0.86/3.7  .97/4.0                                                                             --  0.86/3.7  --                       Gas          3.56/4    3.42/3.25 5.1/3.5                                                                             --  3.42/3.25 --                       Pumping      1.57/5    1.32/4.25 1.47/6.0                                                                            1.9/4                                                                             1.32/4.25 2.54/8                   Mixing       3.81/5.5  5.96/3.5  7.1/4.0                                                                             3.6/3.7                                                                           5.96/3.5  3.81/5.5                 __________________________________________________________________________                 F         G         H         I         J                        __________________________________________________________________________    Type Foaming Gas Injection, N.sub.2                                                                  Chemical Blow                                                                           Chemical Blow                                                                           Gas Injection,                                                                          Gas Injection,                                                                N.sub.2                  Extruder Diameter (mm)                                                                     31.75     31.75     50.8 mm   31.75     31.75                    L/D Ratio    30/1      30/1      28/1      30/1      30/1                     Type Extrusion                                                                             Pressure  Pressure  Pressure  Pressure  Pressure                 Screw Design Zone                                                             Feed         3.81/10   6.6/13    8.25      3.81/10   4.06/10                  Metering     0.86/3.7            Note: long transition                                                                   0.86/3.7  1.02/4                   Gas          3.42/3.25                     3.42/4.25 3.56/4                   Pumping      1.32/4.25 2.54/8    6.6/10    1.32/4.25 1.57/5                   Mixing       5.96/3.5  3.81/5.5            5.96/3.5  3.81/5.5                 __________________________________________________________________________                    A    B   C       D     E   F   G   H   I   J                  __________________________________________________________________________    Temperatures (°C.)                                                     Rear            360  315 329 304 332   250 260 160 326 299 165                Center Rear     382  315 315     260   285 232 188 332 299 177                Center          371  315         260   285 232 201 332 291 165                Center Front    382  315         268   320 254 201 321 288 168                Front           382  315 321 315 273   330 273 201 321 282 171                Adaptor         371  315 315 315 223   315 273 204 357 279 182                X Head          326  325 327     282   320 288 204 360 282 177                Die             326  330 329     282   320 288 204 371 282 177                Melt            387  320 343     125   285 278 210 343 282 178                Screw Speed     80   60  41      72    6   80  70  5   40  25                 Air Gap (meters)                                                                              4.5  4.6 10      4.6   4.6 4.6 4.6 10  4.6 4.5                Wire Size (mm)  0.643                                                                              0.51                                                                              0.51    0.58  0.643                                                                             0.508                                                                             0.51                                                                              0.406                                                                             0.508                                                                             0.51               Wire Speed (m/min.)                                                                           18   41  838     22    34  48.6                                                                              43  30  20  7.6                Wire Preheat (°C.)                                                                     65   132 223     104   65  99  82  150 93  none               Crosshead Melt Pressure (MPa)                                                                 14 (FEP)                                                                           4.9 13.8    4.9   11.7                                                                              9.6 23.4                                                                              4.8 5.2 5.2                Gas Pressure (IKPa)                                                                           0.7  0.7 0.5     0.7   None                                                                              2.1 None                                                                              None                                                                              2.4 2.1                Vacuum (mm Hg)  380  None                                                                              None    None  None                                                                              None                                                                              None                                                                              None                                                                              None                                                                              None               Die (mm)        5.05 1.32                                                                              0.73    1.32  0.914                                                                             1.3 1.3 0.56                                                                              1.6 2.1                Guide Tip (mm)  1.91 0.59                                                                              0.56    0.59  0.685                                                                             0.64                                                                              0.56                                                                              0.43                                                                              0.58                                                                              0.56               Foam Core Size (mm)                                                                           3.30 2.03                                                                              0.83    1.45 to 1.9                                                                         1.15                                                                              2.15                                                                              2.3 0.7 2.28                                                                              ˜2.5         __________________________________________________________________________     Note: Balance of Extruder screw 1/d lengths are transitions and the screw     front tip.                                                               

EXAMPLE 1

A. TFE/HFP copolymer was cube blended with a 5 weight percent boronnitride concentrate (compounded with TFE/HFP copolymer in a 28 mm W&Ptwin screw extruder as described earlier) in the ratio needed to give aproduct with 0.25% boron nitride.

B. A second composition was

prepared from TFE/HFP copolymer by blending a 5 weight boron nitrideconcentrate plus a 0.3 weight % KS-10 concentrate to give 0.25% boronnitride and 330 ppm KS-10.

C. A third composition was prepared from TFE/HFP copolymer by blendingwith a 5 weight percent boron nitride concentrate plus a concentratecontaining 0.3% calcium tetraborate to give 0.25% boron nitride and 125ppm calcium tetraborate.

D. A fourth composition wasprepared from TFE/HFP copolymer by blendingwith a 5 weight % boron nitride concentrate plus a concentratecontaining 0.3% calcium tetraborate and a 0.3 weight % TBSA concentrateto give 0.25% boron nitride and 125 ppm calcium tetraborate plus 330 ppmof TBSA.

These four compositions were extruded onto wire under the conditions ofTable 3, Column A with the following results:

                  TABLE 4                                                         ______________________________________                                                            AFCD                                                      Composition  % V    (M)          cc/cm.sup.3                                  ______________________________________                                        A.           55     381          18,000                                       B.           60     152          312,000                                      C.           55     100          2,800,000                                    D.           58      76          12,000,000                                   ______________________________________                                    

As seen from these results, the KS-10 can be used with boron nitride,and it gives enhanced foam nucleation. Similarly, TBSA can be used inconjunction with boron nitride and calcium tetraborate, and it givesenhanced nucleation.

EXAMPLE 2

TFE/HFP copolymer was blended with a 5% boron nitride concentrate andwith a 0.3% BaS-10 concentrate to give the compositions shown in Table5.

Each composition was foamed onto wire using the conditions of Table 3,Column A.

                  TABLE 5                                                         ______________________________________                                                         Conc.   AFCD                                                 Additive         (ppm)   (M)                                                  ______________________________________                                        None             --      635                                                  Boron nitride    5000    125                                                  BaS-10            125    760                                                  BaS-10            500    100                                                  BaS-10           1000     75                                                  BaS-10           1500    255                                                  ______________________________________                                    

As shown above, BaS-10 is a very effective nucleant at lowconcentrations compared with boron nitride, a traditional nucleatingagent used with TFE/HFP copolymers. It should also be noted that thereis an optimum concentration for the BaS-10 nucleating agent.

EXAMPLE 3

Samples of TFE/HFP copolymer containing several concentrations ofvarious salts of TBSA were prepared by blending virgin resin with theappropriate ratio of concentrate containing 0.3% of the fluorosulfonicacid salt. These compositions were foamed onto wire as described inTable 3, Column A, with the results shown in Table 6. The last columnshows the deviation from the average diameter (3300 micrometers) of thefoam insulated wire.

                  TABLE 6                                                         ______________________________________                                                      Conc.   AFCD           Deviation                                Additive      (ppm)   (M)       % V  (M)                                      ______________________________________                                        Boron nitride (control)                                                                     5500    127       58    ±76                                  ZrS-10        75      685       61   ±127                                                300     387       58   ±127                                                500      76       67    ±76                                                1000     76       65    ±76                                                2000    203       65   ±127                                                3000    203       56   ±127                                  CrS-10        75      635       52    ±50                                                300     431       59    ±76                                                500     101       62    ±50                                                1500    127       62    ±50                                                2000      89 (a)  37   --                                                     3000    (b)       (b)  --                                       CeS-10        63      559       63   ±127                                                250     635       65   ±127                                                500     762       72   ±127                                                1000    381       66    ±76                                                2000    178       67    ±76                                                3000    127       62    ±50                                  KS-10         63      762       78   ±127                                                250     304       65    ±76                                                500     241       66    ±76                                                1000    228       64    ±76                                                2000    (b)       (b)  --                                       HS-10         63      762       61    ±76                                                250     203       65    ±76                                                500     127       64    ±76                                                1000    127       61    ±76                                  AS-10         500     889       60   ±100                                                1000    127       58    ±50                                                2000    139       60   (b)                                      SrS-10        500     139       58   ±100                                                2000    127       59    ±75                                                3000    228       57   ±127                                  CaS-10        500     203       41    ±76                                                1000    228       41   ±100                                                1500    406       41   ±127                                  Zn-10         1000    508       20   ±127                                                2000    381       20   ±127                                                3000    381       20   ±127                                  BaS-10        125     762       20   (c)                                                    500     101       55    ±50                                                1000     76       55    ±50                                                1500    254       40   ±150                                  LS-10         500      178*     55    ±75                                                1000     178*     56    ±75                                  FS-10         75      406       52   ±250                                                150     101       55    ±50                                                300     101       58    ±50                                                500      76       55    ±50                                                1000     76       55    ±59                                  ______________________________________                                         *Cells collapsed to ellipses to the indicated minor diameter. If these        cells were spherical cells, they would be 280 micrometers in diameter.        (a) open cells                                                                (b) gas injector probe plugged                                                (c) no record                                                            

As seen above, all of these fluorosulfonic acid salts (and the HS-10itself) function as nucleating agents. Some are much better than othersand the performance of each one varies with concentration. In additionto cell size and void content variation, there are significantfluctuations in diameter and capacitance.

EXAMPLE 4

A series of samples containing various levels of salts of three othertypes of sulfonic acids and a phosphonic acid were also prepared,extended in TFE/HFP copolymer and foamed onto wire, as described inExample 3, with the results shown in Table 7. The last column shown thedeviation from the average diameter (3300 micrometers) of the foaminsulated wire.

                  TABLE 7                                                         ______________________________________                                                  Conc.   AFCD             Deviation                                  Additive  (ppm)   (M)       % V    (M)                                        ______________________________________                                        BS-9A      500    762       75     (b)                                                  1000    762       62     (b)                                                  2000    381       60      ±75                                              3000    253       54      ±75                                    BS-8       500    254       56     ±100                                              1000    228       57      ±75                                              2000    101       59      ±50                                    KS-8C     1500    635       40     ±200                                              3000    400       40     ±200                                    BTBP      1500     64       80     ±200                                              3000    25-67      ˜70 (a)                                                                       (c)                                        ______________________________________                                         (a) open cells                                                                (b) unstable; diameter control was poor                                       (c) unstable; foaming in crosshead                                       

As seen from the above results, the three barium salts are effective asnucleating agents for TFE/HFP copolymers, whereas the potassium salt isnot.

COMPARATIVE EXAMPLE A

In contrast to Examples 3 and 4, samples containing various levels ofother types of salts (not within the invention) in TFE/HFP copolymerswere prepared in the same manner from concentrates containing 0.3% ofthe salt. These compositions were also foamed onto wire as described inTable 3, Column A with the results shown in Table 8.

                  TABLE 8                                                         ______________________________________                                                   Conc.        AFCD                                                  Additives  (ppm)        (M)     % V                                           ______________________________________                                        LL1121B     500         1016    65                                                       1000         558     46                                                       2000         1016    45                                                       3000         1016    63                                            BC14(06)    500         890     52                                                       1000         762     55                                                       2000         890     55                                                       3000         1016    62                                            BS-12(H)    500         431     57                                                       1000         711     52                                                       2000         889     57                                                       3000         889     57                                            CC-18(H)    500         685     60                                                       1000         1270    62                                                       2000         1524*   63                                            BaC-8       500         635     46                                                       1000         635     45                                            BaC-9       500         1016    42                                                       1000         762     53                                                       1500         889     53                                            ______________________________________                                         *Foam cells blistered outside the insulation surface. All of the              compositions gave large cell size (i.e., greater than 400 micrometers) an     produced unstable capacitance and diameter in extrusion.                 

EXAMPLE 5

Compositions with tetrafluoroethylene(TFE)/perfluoro(propyl vinyl ether)(PPVE) copolymers (TFE/PPVE copolymers) were made up using a 0.3%concentrate of BaS-10 as described in Example 2. These compositions werefoamed onto wire according to the conditions of Table 3, Column A. Theresults are shown in Table 9. The capacitance and diameter stabilityduring extrusion are shown in the last column.

                  TABLE 9                                                         ______________________________________                                                    Conc.   AFCD                                                      Additive    (ppm)   (M)       % V  Remarks                                    ______________________________________                                        TFE/PPVE(1)                                                                   Boron nitride                                                                             5000    300       55   (a)                                        (control)                                                                     BaS-10       63     406       51   (b)                                                     125    330       57   (b)                                                     250    304       55   (b)                                                     500    304       55   (b)                                                    1000    102       55   (b)                                                    2000     89       57   (b)                                                    3000    127       54   (b)                                        TFE/PPVE(2)                                                                   Boron nitride                                                                             5000    255       55   (a)                                        (control)                                                                     BaS-10       500    286       57   (c)                                                    1000    191       58   (c)                                                    2500     51       60   (a)                                                    3000     76       62   (a)                                        ______________________________________                                         (a) Steady extrusion                                                          (b) Head pressure very low in extrusion and some foaming in the crosshead     occurred to make stability of the process borderline. This occurred           because the extruder screw design was not optimized for TFE/PPVE(1).          (c) Extrusion not steady                                                 

As seen from these results BaS-10 is an effective nucleating agent forTFE/PPVE copolymer resins. Note that there is an optimum concentrationrange to achieve the smallest cell size.

EXAMPLE 6

ETFE copolymer containing 2 wt. % boron nitride or varying amounts offluorosulfonic acid salts as indicated in Table 10 was foamed onto wireat about 40 meters/minute according to the conditions of Table 3, ColumnB. This produced a 0.7 mm thick foamed insulation on AWG-24 solid copperwire having capacitance values near 60 pF/m at a foam void level ofabout 60% (Table 10 except for KS-8 and KS-8C). For KS-8 and KS-8C thisproduced a 0.28 mm thick foamed insulation on AWG-24 wire havingcapacitance values near 136 pF/m (a foam void level of about 42%).Relative foaming performance, as indicated by insulation diameter andcapacitance variability and by foam cell size, is shown in Table 10. Thelast column shows the deviation from the average core diameter of 1900micrometers and the deviation from the average capacitance of 62-69pF/m, except for KS-8 and KS-8C wherein the deviations are from anaverage core diameter of 1068 micrometers and an average capacitance of138 pF/m.

                  TABLE 10                                                        ______________________________________                                                  Conc.   AFCD          Deviation                                     Additive  (ppm)   (M)           (M; pF/m)                                     ______________________________________                                        None      None    432           (b)                                           LS-10     750     --            (a)                                                     1500    --            (a)                                                     3000    --            (a)                                           CaS-10    750      76                                                                   1500     51            (c) ± 13; ± 0.3*                                 3000     51                                                         BaS-10    750     178                                                                   1500    178           (c) ± 38; ± 1.5                                   3000    178                                                         ZnS-10    750     432                                                                   1500    432           (d) ± 40; ≧ 15                                3000    432                                                         AS-10     750     500                                                                   1500    432           (d) ± 50; ≧ 15                                3000    483                                                         FS-10     750     635                                                                   1500    635           (c) ± 10; ± 0.3                                   3000    500                                                         KS-8      250     127                                                                   500     114                                                                   1000     76           (c) ± 10; ± 0.3                                   2000     50                                                                   3000     89                                                         KS-8C     250     178                                                                   500     152                                                                   2000     64           (c) ± 10; ± 0.3                                   3000    38- 76                                                      ______________________________________                                         (a) gas injector probe plugged                                                (b) low void content, 32% unstable extrusion                                  (c) extrusion foaming stable                                                  (d) extrusion foaming unsteady                                                *capacitance average of 57 pF/m                                          

EXAMPLE 7

BaS-10 was evaluated as a nucleating agent for ETFE copolymer in a highspeed extrusion (625 m/min.) of thin wall foam-skin insulation on AWG-24solid copper wire. Conditions used are given in Table 3, Column C andthe results are given in Table 11. A dielectric constant of 1.7corresponds to a foam void level of 48%.

                  TABLE 11                                                        ______________________________________                                                  C         Diameter  Foam  AFCD  Ex                                  Additive  (pF/m)    (M)       DC    (M)   St                                  ______________________________________                                        2% BN     121.4 ± 1.0                                                                          1092 ± 50                                                                            1.68  50    (a)                                 (Control Resin)                                                               500 ppm   132.2 ± 0.3                                                                          1049 ± 13                                                                            1.71  50    (b)                                 BaS-10                                                                        1000 ppm  125.3 ± 0.3                                                                          1054 ± 13                                                                            1.63  38    (c)                                 BaS-10                                                                        2000 ppm  131.2 ± 0.3                                                                          1049 ± 13                                                                            1.70  25    (b)                                 BaS-10                                                                        3000 ppm  128.9 ± 1.6                                                                          1049 ± 25                                                                            1.68  50    (b)                                 BaS-10                                                                        ______________________________________                                         (a) Good, steady                                                              (b) A few capacitance spikes. These positive spikes in the capacitance        chart record occurred every 5-8 minutes.                                      (c) Excellent, very steady                                               

As seen from the above results, BaS-10 not only gives small cell sizebut is also improves both diameter and capacitance control in thisminiature foam.

EXAMPLE 8

An E/CTFE copolymer (Halar® 500 available from Ausimont Chemical Co.)was foamed with CHF₂ Cl gas injection using a start-stop extrusionprocedure. This technique was necessary to avoid immediate plugging ofthe gas injection probe (improper screw design) The foaming process wascarried out according to the conditions given in Table 3, Column D.Nucleated compositions were prepared using a 0.3% concentrate of thesalt in the copolymer. The results are given in Table 12.

                  TABLE 12                                                        ______________________________________                                               Conc.   FCC     Foam        AFCD                                       Additive                                                                             (ppm)   (pF/m)  DC    % V   (M)   cc/cm.sup.3                          ______________________________________                                        None   0       98.4    2.01  28    304     336,000                            CaS-10 1500    96.8    2.20  20    203     800,000                            CaS-10 3000    75.5    1.78  43    102   15,000,000                           ______________________________________                                    

As seen from the results, CaS-10 is a very effective foam nucleant.

EXAMPLE 9

HAP-E/TFE, a chemical-blown ETFE copolymer foam resin commerciallyavailable from Chromatics, Inc. (Bethel, Connecticut) was foamed ontowire with and without added BaS-10 using the extrusion setup shown inTable 3, Column E. In each case, the HAP-E/TFE (210 grade) was blendedinto a 50/50 mix with ETFE copolymer (one virgin and one containing 0.3%BaS-10). The results are shown in Table 13.

                  TABLE 13                                                        ______________________________________                                                      No Added Added Nucleant                                                       Nucleant 1500 ppm BS-10                                         ______________________________________                                        Solid AWG-22 Dia (mm)                                                                         0.635      0.635                                              C (pF/m)        91.9       74.2                                               Stability of C (pF/m)                                                                         ±3.3    ±0.7                                            Foam Diameter (mm)                                                                            2.39       2.54                                               D C             2.0        1.85                                               % V             30         35                                                 AFCD (M)        230        38                                                 cc/cm.sup.3 at 33% voids                                                                      38,000     13,000,000                                         ______________________________________                                    

As seen from the results, this nucleating agent is very effective inthis system.

EXAMPLE 10

Chemical-blown ETFE copolymer compositions were prepared by dry blendingpowdered ETFE copolymer with Ficel® and the sulfonic acid salt indicatedin Table 14. The blends were pelletized in a lab scale California PelletMill before evaluation. The compositions were foamed onto wire accordingto conditions given in Table 3, Column E. The results are given in Table14. In each case the amount of blowing agent was 0.38 wt. %.

                  TABLE 14                                                        ______________________________________                                        Additive   BaS-10   CaS-10   KS-8   KS-8                                      Conc.      1000 ppm 1000 ppm 1000 ppm                                                                             3000 ppm                                  ______________________________________                                        C (pF/m)   170.6    175.5    198.4  183.7                                     Foam Diameter                                                                            1.17     1.15     1.10   1.08                                      (mm)                                                                          DC         1.9      1.9      1.9    1.75                                      % V        36       36       36     45                                        AFCD (M)   76       51       51     38                                        cc/cm.sup.3                                                                              1,500,000                                                                              6,500,000                                                                              6,500,000                                                                            18,000,000                                ______________________________________                                    

As seen from the results, these compositions give good quality foam withsmall cell size.

EXAMPLE 11

Blends of 98% of a broad molecular weight distribution linear highdensity polyethylene (0.964 g/cm³) having a melt index of 1.9 (standardmethod 190° C./2.16 kg) and 2% of a high pressure branched polyethylenewith a 0.929 g/cm³ density and a melt index of 1.9, containing variouslevels of sulfonic acid and phosphonic acid salts, were prepared from0.3% concentrates and foamed as an approximately 60% void insulationonto wire using conditions given in Table 3, Column F. The results aregiven in Table 15. The last column shows the capacitance in pF/m and thedeviation from the average diameter (2150 micrometers) of the foaminsulated wire.

                  TABLE 15                                                        ______________________________________                                                Conc.   AFCD                                                          Additive                                                                              (ppm)   (M)         Remarks                                           ______________________________________                                        None    0       360         (a) 55-88 pF/m; ± 150 M                        FS-10   60      229                                                                   150     165                                                                   750     63          (b) 52 ± 0.3 pF/m; ± 50 M                           1500    51                                                                    3000    51                                                            CrS-10  60      203                                                                   150     152                                                                   750     102         (b) 52 ± 0.3 pF/m; ± 50 M                           1500    51                                                                    3000    38                                                             KS-10   60      254                                                                                      (a) 55-88 pF/m; ± 100 M                                150     254                                                                   750     203         (a) 55-88 pF/m; ± 75 M                                  1500    127                                                                                      (b) 52 ± 0.3 pF/m; ± 50 M                           3000    237                                                           BaS-10  63      102                                                                   125     89                                                                    250     76                                                                    500     68          (b) 52 ± 0.3 pF/m; ± 25 M                           1000    64                                                                    3000    64                                                            CaS-10  63      76                                                                    125     76                                                                    250     64          (b) 52 ± 0.3 pF/m; ± 25 M                           1000    51                                                            KS-8    500     51                                                                    1000    43                                                                    2000    33          (b) 52 ± 0.3 pF/m; ± 25 M                           3000    33                                                            KS-6A   500     89                                                                    1000    89                                                                    2000    89          (b) 52 ± 0.3 pF/m; ± 25 M                           3000    51                                                            LS-10   63      152                                                                   125     178                                                                   250     127         (b) 52 ± 0.3 pF/m; ± 101 M                          500     101                                                                   1000    127                                                           KS-8C   500     100                                                                   1000    75                                                                    2000    64          (b) 52 ± 0.3 pF/m; ± 25 M                           3000    40                                                            NTBP    500     127                                                                   1000    76                                                                    1500    25          (b) 56 ± 0.3 pF/m; ± 25 M                           3000    76                                                            NaS-1   500     76          (b) 56 ± 0.3 pF/m; ± 25 M                           1000    64          (b)                                                       3000    51          (b)                                               KS-1    500     203                                                                   1000    178         (a) 52-88 pF/m; ± 75 M                                 3000    152                                                           KS-1(H) 500     330         (a) 69-85 pF/m; ± 50 M                                 1000    152                                                                   2000    89          (b) 56 ± 0.3 pF/m; ± 25 M                           3000    64                                                            BaS-3(H)                                                                              500     175             62 ± 0.7 pF/m; ± 31 M                           1000    38          (b) 60 ± 0.3 pF/m; ± 13 M                           2000    60              59 ± 0.2 pF/m; ± 6 M                     BaP-A   1000    75              59 ± 0.2 pF/m; ± 13 M                                              (b)                                                       2000    100             60 ± 0.2 pF/m; ± 25 M                   NaP-A   500     325         (a) 60-70 pF/m; ± 75 M                                  1000    100             59 ± 0.2 pF/m; ± 25 M                                              (b)                                                       2000    100             59.5 ± 0.2 pF/m; ± 25 M                  BaS-A1(H)                                                                             1000    75              58 ± 0 pF/m; ± 25 M                                                (b)                                                       2000    75              58.5 ± 0.1 pF/m; ± 25 M                  NaS-A(II)                                                                             1000    100             57.5 ± 0 pF/m; ± 38 M                                              (b)                                                       2000    100             56.0 ± 0 pF/m; ± 25 M                   TEAS-10 1000    28          (b) 60 ± 0 pF/m; ± 25 M                             2000    275         (a) 91 ± 16 pF/m/ ± 100                     ______________________________________                                                                        M                                              (a) unstable capacitance                                                      (b) stable capacitance                                                   

As seen from these results, all of these salts act as nucleants, withthe KS-8 and KS-8C being especially effective. Of the S-10 salts, ironand calcium are very effective nucleants.

COMPARATIVE EXAMPLE B

Several other types of organic acid salts were incorporated into thesame polyethylene blend as specified in Example 11 and foamed onto wireusing the conditions of Example 11. The results are shown in Table 16.The last column shows the capacitance and the deviation from the averagediameter (2150 micrometers) of the foam insulated wire.

                  TABLE 16                                                        ______________________________________                                                        AFCD                                                                  Conc.   (% V =                                                        Additive                                                                              (ppm)   60) (M)      Remarks                                          ______________________________________                                        None    --      475                                                           NS-12(H)                                                                              63      508                                                                   250     300                                                                   500     254          (b) 56 to 75 pF/m; ± 152 M                            1000    406                                                                   2000    457                                                           CC-18(H)                                                                              500     457                                                                   1000    457          (b) 56 to 75 pF/m; ± 152 M                            2000    457                                                            BS-12(H)                                                                              600     230                                                                                       (b) 52 to 76 pF/m; ± 100 M                            1200    230                                                                   1800    230          (a)                                                      2940    230          (a)                                              NS-12(H)                                                                              600     300          (c)                                                      1200    380          (b) like BS-12(H)                                Na TCA  1000    304                                                                   2000    280          (b) like BS-12(H)                                        3000    254                                                           ______________________________________                                         (a) Partial plugging of the gas injector probe                                (b) unstable extrusion                                                        (c) fairly stable                                                        

As seen from the above results, these specific salts are not effectiveas nucleants for polyethylene.

EXAMPLE 12

A broad molecular weight distribution, high density polyethylenecopolymer (density=0.945 g/cc, melt index=0.4, standard method 190°C./2.16 kg) containing 0.75% by weight axodicarbonamide blowing agentwas foamed onto wire using the conditions given in Table 3, Column G.This was compared with two, similarly chemically-blown, blendedpolyethylene resins, one with BaS-10 added and one without. As seen fromTable 17, the BaS-10 is a very effective nucleant for this chemicallyblown polyethylene system.

                  TABLE 17                                                        ______________________________________                                                                         PE Blend                                                High       PE         plus 1250 ppm                                Properties Density PE Blend      BaS-10                                       ______________________________________                                        C (pF/m)   6.52       6.04       5.64                                         Foam Diameter                                                                            2.08       2.23       2.28                                         (mm)                                                                          DC         1.77       1.72       1.63                                         % V        33         38         44                                           AFCD (M)   34         41         34                                           Cell Nature                                                                              (a)        (b)        (b)                                          cc/cm.sup.3                                                                              16,500,000 11,500,000 22,000,000                                   ______________________________________                                         (a) irregular and interconnecting cells                                       (b) spherical and distinct separate cells                                

EXAMPLE 13

Polyarylate of the following composition was foamed according to theconditions given in Table 3, Column H.

polyarylate

2000 ppm BaS-10 powder (dry blend)

1250 ppm Expandex® chemical blowing agent

The resultant foamed composition comprised a 0.16 mm wire coating onAWG-26 solid copper wire. This coating was an excellent foam containing30% voids with foam cells of 17 micrometers.

EXAMPLE 14

A nylon blend was foamed according to the conditions given in Table 3,Column I.

Zytel® 301 HS, nylon resin (commercially available)

5000 ppm KS-8, fully compounded

The comparison which was made in extrusion foaming, with and withoutKS-8 as the nucleating agent, is shown in Table 18.

                  TABLE 18                                                        ______________________________________                                                                AFCD                                                  Resin        % V        (M)     cc/cm.sup.3                                   ______________________________________                                        Zytel ® 301HS                                                                           3         762       60                                          Zytel ® 301HS                                                                          65         508     7,800                                         5000 ppm                                                                      KS-8                                                                          ______________________________________                                    

EXAMPLE 15

A melt processible rubber (thermoplastic elastomer) having a dielectricconstant of 10.2 was foamed according to the conditions in Table 3,Column J, producing the results, with and without KS-8 as the nucleatingagent, shown in Table 19.

                  TABLE 19                                                        ______________________________________                                        KS-8 nucleant, ppm                                                                             none     5,000                                               % V              ˜25                                                                               ˜40                                          AFCD (M)         457        89                                                cc/cm.sup.3      4.5 × 10.sup.3                                                                   1 × 10.sup.6                                  ______________________________________                                    

The afore description, including the examples, and the claims whichfollow are intended as a disclosure of the invention and preferredembodiments thereof. There is no intent to limit the invention to onlythose embodiments disclosed, since one skilled in the art will readilyenvision other embodiments from the teaching provided herein.

EXAMPLE 16

Polymer A of this was a copolymer of ethylene and 12% methacrylic acid,40% neutralized with a basic zinc compound, to give a polymer with amelt index of 10. Polymer B of this example was a high pressure,branched polyethylene with a density of 0.929 g/cm³ and a melt index of1.9. A concentrate was made of 4% KS-8 in Polymer A. This concentratewas diluted with a blend of 98% Polymer A and 2% Polymer B to givevarious concentrations of KS-8 in the blends to be extruded, as shown inTable 20. These samples were extruded using the conditions of Table 3,column F. The average foam cell diameter results are shown in Table 20,as are the deviations from the average capacitance.

                  TABLE 20                                                        ______________________________________                                                 Conc.        AFCD                                                    Additive (ppm)        (M)     Remarks                                         ______________________________________                                        None       0          241     ±3 pF/m*                                     KS-8      500         76      ±1.5 pF/m                                    KS-8     1000         51      ±1.5 pF/m                                    KS-8     2000         51      ±0.7 pF/m                                    ______________________________________                                         *Very low void content (20%)                                             

Although the above description and the claims which follow includepreferred embodiments of the invention, it is to be understood thatthere is no intent to limit the invention to the precise constructionsherein disclosed and claimed, and all right is reserved to all changesand modifications coming within the scope of the invention as definedherein.

We claim:
 1. In an improved process for producing a foam of athermoplastic resin composition, the improvement characterized in thatthe process is carried out with a nucleating-effective amount of atleast one thermally stable compound which is selected from the groupconsisting of sulfonic and phosphonic acids and salts thereof, so as toproduce a foam having uniformity of cell size, small cell size, and highvoid content.
 2. Process of claim 1 wherein the nucleating agent isselected from(a) free acids and salts of partially or totallyfluorinated aliphatic sulfonic and phosphonic acids, which optionallymay contain cycloalkyl groups and/or ether oxygen; and (b) free acidsand salts of aromatic sulfonic and phosphonic acids, in which thearomatic ring, optionally, is substituted with alkyl,fluorine-containing alkyl, and/or hydroxyl groups.
 3. Process of claim 1wherein the nucleating agent is of the formula

    [Z(CF.sub.2)×(CF.sub.2 CFX).sub.p (R').sub.y (CH.sub.2).sub.z R03].sub.n M

wherein: the bivalent groups, except for RO₃, may be present in anysequence; Z is selected from CCl₃, CCl₂ 2H, H, F, Cl, F, Cl and Br; eachX, independently, is selected from H, F, Cl and CF3; R is selected fromsulfur and phosphorus; M is selected from H and a metallic, ammonium,substituted ammonium and quaternary ammonium cation; each of x and z,independently, is an integer and is 0 to 20; p is an integer and is 0 to6; y is 0 or 1; x+y+z+p is a positive integer or, if x +y+z+p is 0, thenZ is Cl₃ or CCl₂ H; n is the valence of M; and R' is selected froma C₅₋₆perfluorinated alicyclic ring diradical; a C₁₋₁₆ perfluorinatedaliphatic polyether diradical with repeat units selected from [CF₂ O],[CF₂ CF₂ O], and [CF₂ CF(CF₃)O]; and a substituted or unsubstitutedaromatic diradical, in which case, Z is H.
 4. Process of claim 3 whereinthe nucleating agent contains only two of the diradical units selectedfrom (CF₂ (_(x), (CF₂ CFX)_(p), (R')_(y), and (CH₂)_(z).
 5. Process ofclaim 4 wherein the nucleating agent has a total of no more than 20carbon atoms and M is selected from H, K, Na, Ba, Zr, Cr, Ce, Al, Sr,Ca, Zn, Li, Fe, and triethyl ammonium.
 6. Process of claim 5 wherein thenucleating agent comprises at least one salt of the acid of the formulaF(CF₂)_(x) (CH₂)_(z) SO₃ H, in which x is 6 to 12 and z is 0, 1, or 2.7. Process of claim 1 wherein the thermoplastic resin is selected frompolystyrene, a styrene copolymer, and a blend comprising a styrenepolymer.
 8. Process of claim 1 wherein the thermoplastic resin isselected from copolymers of alpha-olefins and alpha, beta-unsaturatedcarboxylic acids having 3 to 8 carbon atoms, and their metal salts ofGroups I to III of the Periodic Chart of the Elements.
 9. Process ofclaim 1 wherein the nucleating agent is the potassium salt ofperfluorooctane sulfonic acid, and the concentration of nucleatingagent, based on the composition, is 500-3000 ppm.
 10. Process of claim 1wherein the thermoplastic resin is atetrafluoroethylene/hexafluoropropylene copolymer, the average cell sizeis less than 100 micrometers, and the void content is greater than 60%.11. Process of claim 1 wherein the thermoplastic resin is substantiallya polyethylene of high density, the average cell size is less than 100micrometers, and the void content is greater than 50%.
 12. Process ofclaim 1 wherein the thermoplastic resin is anethylene/tetrafluoroethylene copolymer, the average cell size is lessthan 100 micrometers, and the void content is greater than 50%. 13.Process of claim 12 wherein the thermoplastic resin is anethylene/tetrafluoroethylene/perfluorobutyl ethylene copolymer.